1. Field of the Invention
The invention relates to an arrangement for hydraulic actuation of a movable component on a vehicle, for example a trunk lid, a cover or the like, having at least one double-action hydraulic working cylinder, which is attached on one side to the vehicle and on the other side to the movable component whereby one of its working chambers is connected to a passive hydraulic accumulator and the other working chamber is connected to a hydraulic pump, and whereby a line branches off to the tank between said pump and said working cylinder, and into which line there is a pressure relief valve inserted. The invention relates also to a method for hydraulic actuation of a movable component on a vehicle, for example a trunk lid, a cover or the like, through pressurizing a working chamber of a double-action hydraulic working cylinder with a passive hydraulic accumulator and through pressurizing the opposite working chamber of the working cylinder with a hydraulic pump whereby said working cylinder is attached on one side to the vehicle and on the other side to the movable component.
2. The Prior Art
An arrangement and method of this type is known from DE 197 40 029, for example. The passive hydraulic accumulator is therein connected on the piston-side with the working chamber of the working cylinder and in case of a blocked connection between the pump and the working chamber on the rod-side, the pressurization with the hydraulic accumulator effects the outward movement of the working cylinder and thereby the opening of the trunk lid of a vehicle, for example. To close the trunk lid, the connection is opened between the pump and the rod-side working chamber of the cylinder so that the working cylinder retracts and the passive hydraulic accumulator is again simultaneously pressurized.
However, one disadvantage with the described positioning system is the fact that during opening of the trunk lid, the full force of the hydraulic accumulator is released, which causes a very high force at least in partial segments of the opening movement range should an object or a body part of a person be caught in the pivoting path of the trunk lid. Even during impact of the trunk lid onto a solid obstacle, the strong forces of the hydraulic accumulator lead to a considerable danger of damage to the vehicle or the obstacle.
U.S. Pat. No. 4,727,791 discloses a system for the control of a hydraulic single-action cylinder adapted for actuation of vehicle clutches wherein the piston speed of the cylinder may be controlled by two controllable proportional pressure valves. An electronic controllable shut-off valve and a first proportional pressure valve are disposed between the pump of the hydraulic system and the working cylinder whereby the working cylinder is influenced exclusively by the force of the clutch spring on the opposite side of the pump. The second proportional pressure valve is disposed in a line leading to the tank, which branches off from the cylinder supply line between the first proportional pressure valve and the working cylinder precise speed control and stopping of the piston in any desired position is achieved with this very complicated and costly arrangement while safety aspects, emergency operation of the cylinder, and a precise control range of force conditions on the cylinder are not taken into consideration.
In JP 06040233 there is also disclosed a controllable proportional pressure valve used for speed control of the movement of a working cylinder in the height adjustment of a vehicle suspension. However, this proportional pressure valve is disposed in a line that branches off between the pump and an electric controllable shut-off valve that leads to the tank, whereas the working cylinder is located just behind said shut-off valve. The cylinder is here also influenced only by the weight of the vehicle on the opposite side of the pump and the proportional pressure valve is inoperable after closing of the shut-off valve and after completion of the height adjustment process and therefore it cannot assume any safety functions or allow an emergency operation.
The pressure control is designed very similar in this respect in JP 4238993 wherein the maximum pressure may be adjusted by means of a proportional pressure valve but whereby no safety and emergency operations of any kind can be realized. This applies also to the speed control in the remote control operation of a crane according to DE 29 52 963.
It is therefore the object of the invention to improve the type of arrangement and method described above so that the described disadvantages are avoided and that especially the danger of personal injury or damage to the vehicle or other objects may be reduced in a simple and safe manner.
This object is achieved according to the invention in that a check valve is inserted between the pump and the working cylinder blocking in the direction of the pump and whereby a line branches off to the tank between the check valve and the working cylinder and in which line there is installed an electric controllable proportional pressure valve as a pressure relief valve. The proportional pressure valve is a component in which the pressure is proportional to the controlled electric current supplied. Thereby the flow-through pressure in the proportional pressure valve may be kept always slightly higher or lower in a simple manner for the reciprocal movement of the working cylinder through a suitable supply of electric current as it corresponds to the pressure of the hydraulic accumulator. Thus there is of course to be considered the own weight of the actuated component, which according to kinematics mostly acts against the force of the hydraulic accumulator, but it could also work together with this force. Thereby only the differential pressure between the hydraulic accumulator and the pressure determined by the proportional pressure valve affects the vehicle component to be moved on the opposite side and whereby, depending on the effect of the weight of the component, the corresponding pressure must be added to one of the mentioned pressures. In the following, the weight of the component will no longer be explicitly mentioned but it is naturally to be considered in the above sense in all statements about pressure conditions in the system. In general, forces influencing the component may be kept very low, which possibly becomes a factor in case of impact onto an obstacle or when catching a person or objects. The check valve, which is blocking in the direction of the pump and which is inserted between the pump and the fork of the line leading to the tank (in which line there is also inserted the proportional pressure valve), prevents the cylinder from moving in an outward direction in a non-actuated system based on the always-occurring leakage of the pump whereby an unintentional movement of the moved component is prevented, for instance the unwanted opening of a trunk lid. Since the proportional pressure valve controls the pressure in the system between the check valve and the working cylinder, said proportional pressure valve may fulfill its safety function at any time by limiting the maximum pressure in the system.
The proportional pressure valve is designed as a closed valve when without electric power, according to the invention, to avoid unwanted actuation of the component on the vehicle at least in one direction in case of electric power failure.
To guarantee during emergency manual operation and in case of hydraulic pump failure that the displaced component does not immediately spring back into the position in which it was before the pump failure, there branches off a line to the tank between the working cylinder and the fork of the line, in which line the proportional pressure valve is installed, and in which a post-suction check valve is placed blocking in the direction of the tank. Thereby hydraulic fluid may be moved manually through suction from the tank into the working cylinder and after releasing the component, it remains fixed in position because of the now locked post-suction check valve and the preferably closed proportional pressure valve being without electric power.
The passive hydraulic accumulator is advantageously designed as a spring-operated accumulator to make the arrangement independent on the current surrounding temperatures.
According to an additional characteristic of the invention, there are control electronics provided in which a program is stored for a varying electric power supply to the proportional pressure valve to adapt to the changing conditions in the hydraulic accumulator and/or the kinematics of the component that is moved above the working cylinder. During movement of the trunk lid or the like, the least possible excessive force is thereby guaranteed for the movement and guaranteed is thereby also the optimum passive protection against danger of injury by clamping down or damage to objects.
The object stated in the beginning is achieved by the method for hydraulic actuation of a movable component on a vehicle in that during the forward movement of the working cylinder, the pressure in the opposite working chamber is kept at a low range below the pressure of the hydraulic accumulator. Thereby only a very low differential pressure influences the component to be moved on the vehicle, namely the one between the hydraulic accumulator and the pressure determined by the proportional pressure valve on the opposite side, which is made available for the retracting movement of the pump, so that the forces at the component may be kept very low.
With the same effect and as just described, there is proposed in the method for hydraulic actuation of a movable component on a vehicle, according to an additional characteristic of the invention, that during the return movement of the working cylinder, the pressure in the working chamber that is connected to the pump is kept at a low range above the pressure of the hydraulic accumulator.